It is common in automobile traffic control to use pavement markings for directing vehicles. Typically, solid lines and skip lines are formed on the surface of pavement to guide the drivers of vehicles in safe traffic flow arrangements.
In order to reduce accidents involving vehicles running off of the road or out of a lane, pavement markers are used that produce an audible and vibratory effect when a wheel of a vehicle drives over the markings. One such pavement marker involves including a small bump at intervals on a base line of the highway. The bumps may be applied by extruding a molten or uncured lump of a specially designed material onto the base line of pavement striping. Upon curing, the lump of material becomes a solid bump and produces the audible vibratory effect when driven over. This bump line approach has been mostly avoided by contractors due to slow application speeds, high material consumption, and excessive cure times as much as fifteen minutes or more. Other problems exist with variations in size and shape of the bump that may be produced, for example, by temperature and viscosity fluctuations.
It is known that objects may be embedded into a pavement striping to increase light reflectivity in order to make the pavement striping more visible in darkness. As an example, reflective beads such as glass spheres have been applied to pavement striping when it the striping is still in a molten state. The beads that are used to reflect light may be translucent and therefore retroreflective, or the beads may be formed of reflective material. This is effective particularly when the beads are elevated above the pavement surface so that they are not submerged in wet conditions. However, merely embedding retroreflective beads in pavement striping fails to produce a sufficient audible vibration from the striping when a vehicle crosses over the striping.
As another example, reflective pavement markers, such as those described in U.S. Pat. No. 3,418,896 to Rideout, have been embedded into molten pavement striping. Rideout discloses reflective pavement markers that produce rumbles or bumps when vehicle wheels roll over them. Rideout extrudes a “rod” of plastic material, applies glass spheres to the rod and cuts the rod into the desired thickness. The pavement markers of Rideout have flat upper and lower surfaces and vertical side walls coated with glass spheres. The upper flat surface of the Rideout pavement marker is not reflective. When the glass spheres wear off of the side walls, the marker loses its reflectivity and must be replaced. Although Rideout discloses dropping his pavement markers “onto a tacky binder layer with one of the flat sides down,” Rideout fails to disclose a method or an apparatus for dispensing the pavement markers automatically.
Most resin systems suitable for pavement markings are made of relatively sticky materials, particularly sticky in hot weather, with low temperature softening points. With no exposed beads on the upper surfaces of the pavement markings to act as a barrier between the resin layers in an upwardly extending stack of the products, the products likely would adhere to each other and be difficult to separate.
U.S. Pat. No. 4,279,534 to Eigenmann discloses a method and apparatus for applying asymmetrical retroreflective elements to a carrying layer such as a traffic paint film. However, Eigenmann fails to teach a method for applying pavement markers of a larger size to molten pavement striping while avoiding the undesirable defects in the base line material that can occur at higher application speeds. For example, a straight drop of a pavement marker from a vehicle traveling at or above 3 miles per hour (mph) can result in skidding of the marker, which forms a puddle in the base line material. Even at speeds as slow as 1 mph and assuming an effectively disc-shaped pavement marker, if the front, or leading, edge of the pavement marker hits the base line first, the marker tends to flip upside down due to the combination of forces applied by the striping to the marker. Alternatively, if the pavement marker is dropped with too great of a rearward tilt, the marker might bounce, leaving a divot in the base line, and might flip over. My invention includes a pavement marker constructed of material capable of partially melting and fusing with a molten highway striping.
Thus, this invention addresses the inadequacies of the prior art described above and provides improved pavement markers for the audible and retroreflective marking of highways, and the apparatus and process of applying the markers to pavement striping on highways.